1. Field of the Invention
The present invention relates to a closed tank system in which a shut-off valve is provided in a communication passage between a fuel tank that stores fuel to be supplied to an internal-combustion engine mounted on a vehicle, and a canister that adsorbs evaporative fuel generated in the fuel tank.
2. Description of the Related Art
For example, Patent document 1 (Japanese Unexamined Patent Application Publication No. 2015-081528) discloses a closed tank system in which a shut-off valve is provided in a communication passage between a fuel tank which stores fuel to be supplied to an internal-combustion engine mounted on a vehicle, and a canister which adsorbs evaporative fuel generated in the fuel tank. The closed tank system disclosed in Patent document 1 is adapted to carry out control for allowing the shut-off valve to be opened during oil supply, or when the internal-combustion engine is in operation and a tank inner pressure exceeds a predetermined threshold. Such a closed tank system is generally used in a vehicle such as a plug-in hybrid car in which an internal-combustion engine is less frequently used.
The fuel tank composing the closed tank system disclosed in Patent document 1 is provided with a member called a fill-up limiting valve. The fill-up limiting valve is disposed to lie in the communication passage between the fuel tank and the shut-off valve. The fill-up limiting valve is adapted to operate to close the valve by allowing a float to float on the fuel when a fuel level reaches a predetermined full tank liquid level.
Incidentally, in scenes of refueling for the fuel tank, supplemental refueling is additionally carried out in some cases after the fuel level reaches the full tank liquid level. Where such supplemental refueling is carried out, there is a risk that, when control for allowing the shut-off valve to be opened is carried out, fuel in liquid form reaches the canister through the shut-off valve. This will be explained below. When the supplemental refueling is carried out, the fuel level reaches an over-full tank liquid level that exceeds the full tank liquid level. This allows the fill-up limiting valve to be brought into a state wetted with the fuel. When control for allowing the shut-off valve to be opened is carried out in this state, a differential pressure is generated between an upstream side (high pressure side in the fuel tank) and a downstream side (low pressure side in the communication passage) with a valve part of the fill-up limiting valve as a boundary. Accordingly, the differential pressure causes the fuel level in the fill-up limiting valve to rise. At this time, movement of the float allows the valve part of the fill-up limiting valve to start closing. However, the movement of the float is preceded by the fact that the differential pressure causes the fuel to be sucked out of the fuel tank to the downstream side (low pressure side in the communication passage).
As a result, when the control for allowing the shut-off valve to be opened is carried out where the supplemental refueling causes the fuel level to reach the over-full tank liquid level, there has been a risk that the fuel in liquid form reaches the canister through the shut-off valve.
The present invention has therefore been made in view of the above actual circumstances, and an object of the invention is to provide a closed tank system capable of preventing fuel in liquid form from reaching a canister through a shut-off valve.